1. Field
One or more embodiments of the invention relate to a zoom lens and an electronic device employing the same, and more particularly, to a zoom lens used in, for example, a video camera, a digital camera, a camera-equipped mobile phone, an information portable terminal, or the like.
2. Description of the Related Art
In the related art, a focusing method of zoom lens in the nearest position (i.e., focusing on an object in the nearest position) includes (1) a focusing method using a first lens group and (2) a focusing method using a lens group other than the first lens group.
The zoom lens using the focusing method (1) has a simple structure and a relatively simple design. However, in particular, in the case where the foremost lens group of the zoom lens is a lens group having a positive refractive power and having a wide angle, the focusing method (1) has a problem in that a diameter of a foremost lens of the foremost lens group is increased.
On the other hand, as an example of the focusing method (2), there are methods for resolving the above-mentioned problem. In particular, in the case where the foremost lens group of zoom lens is a lens group having a positive refractive power, and focusing is performed using a second lens group having a negative refractive power, the above-mentioned problem is easily resolved, and thus the focusing method (2) is particularly known as being appropriate for a zoom lens of a high magnification (for example, Japanese Unexamined Patent Publication No. 05-142475, Japanese Unexamined Patent Publication No. 06-75167, etc.).
In addition, as an example of a zoom lens using the focusing method (2), a known zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, which are disposed in this order from an object side, and focusing is performed through the third lens group (for example, Japanese Unexamined Patent Publication No. 10-133109, Japanese Unexamined Patent Publication No. 10-133111, Japanese Unexamined Patent Publication No. 10-133112, Japanese Unexamined Patent Publication No. 11-295597, etc.).
Furthermore, as an example of a zoom lens using the focusing method (2), a known zoom lens includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power, which are disposed in this order from an object side, and focusing is performed by moving a negative lens included within the third lens group toward an image surface side (for example, Japanese Unexamined Patent Publication No. 2011-247962, Japanese Unexamined Patent Publication No. 2011-247963, and Japanese Unexamined Patent Publication No. 2011-247964).
However, in the above examples, in which a lens group having a positive refractive power precedes a second lens group having a negative refractive power, a focusing method that performs focusing through the second lens group has a problem as follows. In a zoom lens in which a lens group having a positive refractive power precedes a second lens group having a negative refractive power, since the second lens group having the negative refractive power generally affects the magnification within the whole optical system, the second lens group has a large number of lenses and is large in mass. Accordingly, it is difficult to control the second lens group to be minutely moved forward and backward. In particular, the second lens group is not appropriate for auto-focusing through the detection of blur of an imaging element.
In addition, a zoom lens—in which a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are disposed in this order from an object side and focusing is performed through the third lens group—has a large number of lenses, and thus the focusing method has the above-mentioned problem.
Furthermore, a zoom lens—in which a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a positive refractive power are disposed in this order from an object side and focusing is performed by moving a negative lens included within the third lens group toward an image side surface—has only two magnification groups, and thus the focusing method is at a disadvantage in terms of high magnification. To achieve a high magnification ratio, a satisfactory optical performance of the zoom lens may not be maintained, or the optical system may increase in size.